The present invention relates to tires with improved bead regions and in particular to heavy duty tires such as are used for trucks and buses.
The tire of the present invention includes in the bead region a filler or chafer strip laid around the outside of the bead over the carcass ply or plies and extending from beneath the bead hoop to a point radially outwards of the bead hoop. This chafer strip is usually made of cut edged weftless tire cord fabric laid with the cords at an acute angle (bias angle) to the centerline of the bead hoop.
In use of the vehicle cyclically varying tensile and compression forces are applied to the radially outer edge of the filler strip and tire life can be reduced by failure in the edge region of the filler strip known as filler edge looseness. This failure is a a failure of the bond between the cords at their ends and the rubber compound of the tire can result in a complete tire failure.
It has been suggested in UK Patent Specification No. 2141676 A to use looped edge fabric to avoid the cut edges of the cords and reduce this problem by improving the resistance of the cord at the filler strip edges to filament separation.
It is an object of the present invention to reduce the filler edge looseness problem by a different approach and to provide a construction which materially reduces the failure inducing forces in the filler strip.
The present invention provides a tire having a pair of axially spaced-apart bead regions each reinforced by an annular bead hoop around which one edge of a carcass reinforcing ply is wrapped and a filler strip positioned in the axially outer region of the bead which extends circumferentially around the bead. The filler strip has one edge radially inwards of the bead hoop and one edge axially outwards of the bead hoop and comprises substantially weftless tire cord fabric laid with the cords at an acute angle to the circumferential centerline of the bead hoop wherein the filler strips in both beads have their cords laid at an acute angle to the same specified direction circumferentially such that the cords of one filler strip are substantially parallel to the cords of the other filler strip. The tire has an external direction marker in the same circumferential direction to the specified direction so that in use the tire may be fitted to a vehicle with the marker in the opposite direction to the greatest torque force applied to the tire from the wheel.
In the case of a non-driven wheel, the greatest torque force from the wheel is the torque from the brakes and in the case of a driven wheel the greatest torque force leading to tire failure is that due to the drive torque, although the braking force sometimes is the larger torque being applied of a short duration.
The filler strip may have its radially inner edge beneath the bead hoop or may be alongside it in the heel region of the tire. The radially outer edge of the filler strip is preferably radially outwards of the edge of the carcass ply so that the filler strip overlies the said edge. The radially outer edge of the filler strip may be a folded edge with the filler strip folded back on itself.
The filler strip may comprise cut edge tire fabric or may comprise a narrow band formed by a single cord which extends back and forth across the band in a zig-zag formation to form a band substantially of a single cord in thickness.
The assembly is such that the range of stress applied to the filler strips at their radially outer edges are reduced because the predominant large torque forces what would otherwise lead to filler edge looseness are applied to the filler strip in predetermined directions so that the cords act in the most efficient manner.
More then one filler strip may be used at each side of the tire and any known filler strip material including steel cords may be utilized.
Hitherto, while cords have been placed in the same directions at both sides of the tire it has been without the important tire marker to provide correct usage and such matched directions have been purely to ease production problems such as rolling down of components during tire assembly. The marker on the tire may be on the sidewall or a directional tire tread pattern.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.